A mask assembly typically includes a relatively rigid shell, e.g., a frame, and a patient interface, e.g., a pair of nozzles (which may be in the form of nasal pillows, nasal prongs, cannulae, or nasal puffs) or a cushion (nasal or full-face), that is supported by the rigid shell and structured to deliver pressurized gas to the patient or user in a comfortable, sealed manner. The mask assembly is usually held in place using a headgear assembly.
In some applications, there may be a clinical requirement to provide the mask assembly with one or more safety devices, such as means for CO2 washout, vents, anti-asphyxia valves and the like. In some cases, these additional components are assembled between the gas delivery conduit and the mask assembly. Problems with prior art assemblies may include:
(a) inadvertent assembly without one or more of the safety devices;
(b) incorrect assembly/alignment; and/or
(c) incorrect re-assembly following inadvertent dis-assembly during the course of treatment.
Flow generators typically deliver pressurized breathable gas (air) to a patient wearing the mask assembly. In CPAP treatment, gas is delivered to the patient's airways at about 2-30 cm H2O above atmospheric pressure. The flow generator is generally connected to flexible tubing (air delivery tube) that is secured to the mask assembly worn by the patient. If the flow generator's operation is interrupted as a result of power outage or other mechanical/electrical failure, there may be a significant build up of carbon dioxide in the mask as the patient's exhaled air is not washed out of outlet vents that are usually provided to the mask assembly. This may present a health risk to the patient.
Several patents have addressed this risk, e.g., by use of a safety valve for gas or air delivery mask assemblies. See, e.g., U.S. Pat. No. 3,796,216 to Schwarz, and U.S. Pat. No. 5,438,981 to Starr et al., as well as PCT international application no. PCT/AU97/00849.